The invention is based on an optical transmission system and transmitters and receivers for an optical transmission system for the transmission of frequency-coded signals.
The as yet unpublished German Application 197 48 756.4 has disclosed a receiver for spectrally-coded optical signals. A transmission network for coded optical signals comprises optical transmission lines, optical splitters and optionally optical amplifiers, and serves to transmit coded, multiplexed optical signals. Each transmitter contains a coder in which the signals to be transmitted are coded before being transmitted into the optical transmission network. The coding is effected optically, for example by frequency coding using an optical filter. Each receiver which wishes to receive the data of a specific transmitter must contain a decoder tuned to the coder of this specific transmitter. In the simplest case, the frequency bands which transmit optical signals and the frequency bands which block optical signals are the same both in the coder and the decoder. The known CDMA (Code Division Multiple Access) processes are primarily suitable for the transmission of bit rates which are not too high ( greater than 155 MBit/s). The CDMA process is suitable for use as a multipoint-to-multipoint network, such as for example a LAN. If one considers the resolution in the individual receivers, up to approximately 32 channels can be transmitted in parallel in this process.
The object of the invention is to propose a simple multipoint-to-multipoint connection system which makes a large number of channels available and can be implemented using simple components.
The optical transmission system according to the invention has the advantage of combining narrow-band CDMA transmission with WDM (Wavelength Division Multiplex) transmission and thus making up to 256 channels available multipoint-to-multipoint. Advantageously, a combined process of this kind can be implemented using transmitters of simple construction with no special demands on the specification, e.g. the wavelength stability, of the transmitting laser. As the transmitting modules are not subject to any special demands, simple and cost-efficient implementations are possible. Advantageously, an optical transmission system for frequency-coded signals is created in that the coding is generated by modulation of the injection current of the laser diode and, by means of special modulation with the data signal, a simple detection in the receiver is possible. The special modulation in the transmitter and the detection thereof in the receiver facilitate a very simple construction of the receiver. In particular, the use of a differential amplifier, which is costly to implement and sensitive in respect of its tuning, is avoided. The transmitters and receivers used for the optical transmission system are of very simple construction.
An exemplary embodiment of the invention is illustrated in the drawings and explained in detail in the following description.